scholarly journals Inflow-rotor interaction in Tesla disc turbines: Effects of discrete inflows, finite disc thickness, and radial clearance on the fluid dynamics and performance of the turbine

2018 ◽  
Vol 232 (8) ◽  
pp. 971-991 ◽  
Author(s):  
Sayantan Sengupta ◽  
Abhijit Guha
Keyword(s):  
Fluid Dynamics ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Radial Clearance ◽  
Dynamic Simulations ◽  
Partial Admission ◽  
Inflow Condition ◽  
And Performance ◽  
Dynamics Simulations ◽  
Optimum Formula

The article establishes the physics of the complex interaction of discrete multiple inflows with the stationary shroud and the rotating channel of a Tesla disc turbine. Using a large number (150) of separate, fully three-dimensional computational fluid dynamic simulations, we demonstrate the (sometimes dramatic) role of four important input parameters, namely the number of nozzles ([Formula: see text]), rotational speed of the discs (Ω), radial clearance between the rotor and the shroud ([Formula: see text]), and disc thickness ( dt), in the fluid dynamics and performance of a Tesla turbine. An increase in [Formula: see text] or [Formula: see text] assists in the attainment of axisymmetric condition at rotor inlet. Ω influences significantly the distribution of radial velocity including the fundamental shape of its z-profile (parabolic, flat or W-shaped). The paper demonstrates the existence of an optimum [Formula: see text] for which the efficiency of the rotor (η) is maximized. Present computational fluid dynamics simulations for many combinations of [Formula: see text] and Ω establish that the η versus Ω curves, for each fixed value of [Formula: see text], are of the shape of an inverted bucket. With increasing [Formula: see text], the operable range of Ω decreases, the buckets become more peaky and the maximum possible η increases substantially (by a factor of 2 in the example calculation shown). The present systematic work thus demonstrates quantitatively, for the first time, that an axisymmetric rotor inflow condition represents the best possible design for the rotor. It is further shown that, as the disc thickness is increased, the efficiency may decrease substantially (even dramatically) and its maxima occur at lower rotational speeds. Chamfering of the disc edge or partial admission decreases the turbine efficiency. Thus, small disc thickness, flat disc edge, full nozzle opening, optimum radial clearance, and inlet condition as close to axisymmetry as is possible are recommended for the design of an efficient Tesla disc turbine.

Analysis of Velopharyngeal Functions Using Computational Fluid Dynamics Simulations

2019 ◽  
Vol 128 (8) ◽  
pp. 742-748 ◽  
Author(s):  
Hanyao Huang ◽  
Xu Cheng ◽  
Yang Wang ◽  
Dantong Huang ◽  
Yuhao Wei ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Computational Fluid Dynamic Simulation ◽  
Dynamic Features ◽  
Upper Airways ◽  
Dynamic Simulations ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

Objectives: Competent velopharyngeal (VP) function is the basis for normal speech. Understanding how VP structure influences the airflow during speech details is essential to the surgical improvement of pharyngoplasty. In this study, we aimed to illuminate the airflow features corresponding to various VP closure states using computed dynamic simulations. Methods: Three-dimensional models of the upper airways were established based on computed tomography of 8 volunteers. The velopharyngeal port was simulated by a cylinder. Computational fluid dynamics simulations were applied to illustrate the correlation between the VP port size and the airflow parameters, including the flow velocity, pressure in the velopharyngeal port, as well as the pressure in oral and nasal cavity. Results: The airflow dynamics at the velopharynx were maintained in the same velopharyngeal pattern as the area of the velopharyngeal port increased from 0 to 25 mm2. A total of 5 airflow patterns with distinct features were captured, corresponding to adequate closure, adequate/borderline closure (Class I and II), borderline/inadequate closure, and inadequate closure. The maximal orifice area that could be tolerated for adequate VP closure was determined to be 2.01 mm2. Conclusion: Different VP functions are of characteristic airflow dynamic features. Computational fluid dynamic simulation is of application potential in individualized VP surgery planning.

Stent-Assisted Coil Embolization and Computational Fluid Dynamics Simulations of Bilateral Vertebral Artery Dissecting Aneurysms Presenting With Subarachnoid Hemorrhage

Neurosurgery ◽  
2012 ◽  
Vol 71 (6) ◽  
pp. E1192-E1201 ◽  
Author(s):  
Kenichi Kono ◽  
Aki Shintani ◽  
Takeshi Fujimoto ◽  
Tomoaki Terada
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Subarachnoid Hemorrhage ◽  
Vertebral Artery ◽  
Coil Embolization ◽  
Fluid Dynamic ◽  
Single Session ◽  
Dynamic Simulations ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

ABSTRACT BACKGROUND AND IMPORTANCE: A vertebral artery dissecting aneurysm (VADA) is a relatively rare cause of subarachnoid hemorrhage. Bilateral VADAs are even rarer, and management strategies are controversial. We report a case of bilateral VADAs presenting with subarachnoid hemorrhage. We treated the patient by stent-assisted coil embolization of both aneurysms at a single session on the basis of results of preoperative computational fluid dynamic simulations. CLINICAL PRESENTATION: A 48-year-old man presented with subarachnoid hemorrhage resulting from bilateral VADAs. We treated the patient by stent-assisted coil embolization of both aneurysms at a single session. Before the treatment, we performed computational fluid dynamics simulations to predict the ruptured side. We also estimated the increase in wall shear stress on an aneurysm in case of trapping of another aneurysm, which might cause enlargement and rupture of the aneurysm. The treatment was performed successfully. The patient remains neurologically intact at 14 months from the onset. CONCLUSION: Stent-assisted coil embolization of subarachnoid hemorrhage with bilateral VADAs for both sides is a reasonable treatment because it prevents rebleeding and preserves bilateral vertebral arteries without increasing hemodynamic stress. To the best of our knowledge, this is the first report to describe this type of treatment for bilateral VADAs with subarachnoid hemorrhage. Computational fluid dynamics simulations may be useful for developing treatment strategies for aneurysms.

scholarly journals Enhancing Radiation Detection by Drones through Numerical Fluid Dynamics Simulations

Sensors ◽  
2020 ◽  
Vol 20 (6) ◽  
pp. 1770 ◽  
Author(s):  
Fabio Marturano ◽  
Jean-François Ciparisse ◽  
Andrea Chierici ◽  
Francesco d’Errico ◽  
Daniele Di Giovanni ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Nuclear Power ◽  
Situational Awareness ◽  
Fluid Dynamic ◽  
Low Cost ◽  
Radiation Detection ◽  
First Responders ◽  
Decision Makers ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

This study addresses the optimization of the location of a radioactive-particle sensor on a drone. Based on the analysis of the physical process and of the boundary conditions introduced in the model, computational fluid dynamics simulations were performed to analyze how the turbulence caused by drone propellers may influence the response of the sensors. Our initial focus was the detection of a small amount of radioactivity, such as that associated with a release of medical waste. Drones equipped with selective low-cost sensors could be quickly sent to dangerous areas that first responders might not have access to and be able to assess the level of danger in a few seconds, providing details about the source terms to Radiological-Nuclear (RN) advisors and decision-makers. Our ultimate application is the simulation of complex scenarios where fluid-dynamic instabilities are combined with elevated levels of radioactivity, as was the case during the Chernobyl and Fukushima nuclear power plant accidents. In similar circumstances, accurate mapping of the radioactive plume would provide invaluable input-data for the mathematical models that can predict the dispersion of radioactivity in time and space. This information could be used as input for predictive models and decision support systems (DSS) to get a full situational awareness. In particular, these models may be used either to guide the safe intervention of first responders or the later need to evacuate affected regions.

Propulsive Efficiency of the Underwater Dolphin Kick in Humans

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
Alfred von Loebbecke ◽  
Rajat Mittal ◽  
Frank Fish ◽  
Russell Mark
Keyword(s):  
Fluid Dynamic ◽  
Three Dimensional ◽  
Underwater Video ◽  
Dynamic Simulations ◽  
Slender Body Theory ◽  
Propulsive Efficiency ◽  
Video Footage ◽  
Wide Range ◽  
Dolphin Kick ◽  
Body Theory

Three-dimensional fully unsteady computational fluid dynamic simulations of five Olympic-level swimmers performing the underwater dolphin kick are used to estimate the swimmer’s propulsive efficiencies. These estimates are compared with those of a cetacean performing the dolphin kick. The geometries of the swimmers and the cetacean are based on laser and CT scans, respectively, and the stroke kinematics is based on underwater video footage. The simulations indicate that the propulsive efficiency for human swimmers varies over a relatively wide range from about 11% to 29%. The efficiency of the cetacean is found to be about 56%, which is significantly higher than the human swimmers. The computed efficiency is found not to correlate with either the slender body theory or with the Strouhal number.

scholarly journals Three-dimensional multiphase flow computational fluid dynamics models for proton exchange membrane fuel cell: A theoretical development

2017 ◽  
Vol 9 (1) ◽  
pp. 3-25 ◽  
Author(s):  
Jean-Paul Kone ◽  
Xinyu Zhang ◽  
Yuying Yan ◽  
Guilin Hu ◽  
Goodarz Ahmadi
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Fuel Cell ◽  
Multiphase Flow ◽  
Proton Exchange Membrane ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Proton Exchange ◽  
Dynamics Models ◽  
Exchange Membrane

A review of published three-dimensional, computational fluid dynamics models for proton exchange membrane fuel cells that accounts for multiphase flow is presented. The models can be categorized as models for transport phenomena, geometry or operating condition effects, and thermal effects. The influences of heat and water management on the fuel cell performance have been repeatedly addressed, and these still remain two central issues in proton exchange membrane fuel cell technology. The strengths and weaknesses of the models, the modelling assumptions, and the model validation are discussed. The salient numerical features of the models are examined, and an overview of the most commonly used computational fluid dynamic codes for the numerical modelling of proton exchange membrane fuel cells is given. Comprehensive three-dimensional multiphase flow computational fluid dynamic models accounting for the major transport phenomena inside a complete cell have been developed. However, it has been noted that more research is required to develop models that include among other things, the detailed composition and structure of the catalyst layers, the effects of water droplets movement in the gas flow channels, the consideration of phase change in both the anode and the cathode sides of the fuel cell, and dissolved water transport.

Investigation of the Flow Field on a Transonic Turbine Nozzle Guide Vane With Rim Seal Cavity Flow Ejection

2009 ◽  
Author(s):  
M. Pau ◽  
G. Paniagua
Keyword(s):  
Flow Field ◽  
Static Pressure ◽  
Numerical Study ◽  
Guide Vane ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Cavity Flow ◽  
Trailing Edge ◽  
Dynamic Simulations ◽  
Purge Flow

Ensuring an adequate life of high pressure turbines requires efficient cooling methods, such as rim seal flow ejection from the stator-rotor wheel space cavity interface, which prevents hot gas ingress into the rotor disk. The present work addresses the potential to improve the efficiency in transonic turbines at certain rim seal ejection rates. To understand this process a numerical study was carried out combining computational fluid dynamic simulations (CFD) and experiments on a single stage axial test turbine. The three dimensional steady CFD analysis was performed modeling the purge cavity flow ejected downstream of the stator blade row, at three flow regimes, subsonic M2 = 0.73, transonic M2 = 1.12 and supersonic M2 = 1.33. Experimental static pressure measurements were used to calibrate the computational model. The main flow field-purge flow interaction is found to be governed by the vane shock structures at the stator hub. The interaction between the vane shocks at the hub and the purge flow has been studied and quantitatively characterized as function of the purge ejection rate. The ejection of 1% of the core flow from the rim seal cavity leads to an increase of the hub static pressure of approximately 7% at the vane trailing edge. This local reduction of the stator exit Mach number decreases the trailing edge losses in the transonic regime. Finally, a numerically predicted loss breakdown is presented, focusing on the relative importance of the trailing edge losses, boundary layer losses, shock losses and mixing losses, as a function of the purge rate ejected. Contrary to the experience in subsonic turbines, results in a transonic model demonstrate that ejecting purge flow improves the vane efficiency due to the shock structures modification downstream of the stator.

scholarly journals Design and Performance Analysis of Contra-rotating Pumpjet Propulsor under Condition of Torque Unbalance

2018 ◽  
Vol 167 ◽  
pp. 03006
Author(s):  
Xiao-er Wang ◽  
Zhen-shan Zhang ◽  
Meng Zhang
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Design Method ◽  
Three Dimensional ◽  
Underwater Vehicle ◽  
Inverse Design ◽  
Parameter Design ◽  
Power Difference ◽  
Inverse Design Method ◽  
And Performance

In order to balance the torque of front rotor and rear rotor of underwater vehicle, the analysis of the speed triangles at the inlet and outlet of the front and rear rotor has been done. Then, the thought of using contra-rotating pumpjet to achieve the objective was raised. The stator is installed behind the rear rotor so as to ensure the overall torque of the propulsor balance, at the same time, the stator can also support the shroud of the propulsor. the parameter design of the rotor and the stator has been carried out by using the three dimensional inverse design method. At last, the performance of the designed pumpjet propulsor is obtained when it is installed on the underwater vehicle By using computational fluid dynamics. The results show that the total torque of the propulsor is reduced to 1.8 N * m on the design point although the power difference ratio of the front rotor and the rear rotor is 20%. The torque ratio is also reduced from 4.6% to 0.4%, which is good to meet the propulsor balance requirement and verifies the 3-D design method of pumpjet is effective.

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